It is now common for a vehicle's steering wheel to support various electrical devices, such as audio system controls, a horn actuation switch, and a supplemental inflatable restraint (SIR) module. A contact plate may be employed to maintain electrical communication between the vehicle's electrical infrastructure and the audio system controls, the horn actuation switch, and other such steering-wheel mounted inputs. However, an SIR coil assembly is commonly employed to provide a more reliable hardwire connection with the SIR module. A generalized SIR coil assembly includes a stator body, a rotor body, and a flat ribbon cable coiled between the stator body and the rotor body (commonly referred to as an “SIR coil” or a “clock spring roll”). The stator body of the SIR coil assembly is fixedly attached to the steering column housing, and the rotor body is affixed to the steering wheel or the rotatable steering column shaft. As a driver turns the vehicle's steering wheel, the rotor body of the SIR coil assembly rotates relative to the stator body. The coiled ribbon cable furls and unfurls as needed to accommodate this rotational movement.
Vehicular steering wheel and column assemblies have been extensively engineered to provide desirable steering characteristics. Despite this, conventional steering wheel and column assemblies may still permit minor torsional vibrations to be transmitted through the steering column shaft to the steering wheel. Such vibrations may be produced by various periodic sources at the rotating corners of the vehicle (e.g., tires, wheels, brake rotors, bearing hub assemblies, etc.), including such conditions as imbalance and non-uniform tires, and consequently may be produced even when the vehicle is traveling over a relatively smooth road. This vibratory condition is commonly referred to as “smooth road shake” or, more simply, “SRS.” In general, SRS may be characterized by the unwanted dynamic rotational movement of the steering wheel at or above thresholds perceptible to a driver; e.g., occurring on the order of a few fractions of a degree (e.g., 1.5 minutes) generally at frequencies ranging from approximately 8 to 20 hertz, especially when the vehicle is operated over a range of speeds of approximately 80 to 160 kilometers per hour. Although this rotational movement is relatively minor, it is readily perceptible to a driver and consequently undesirable. Devices have been produced that attempt to minimize SRS by providing a clamping force around the steering wheel shaft; however, such devices have been limited in various respects. For example, such devices tend to be inherently resilient for small angular displacements and consequently store, rather than dissipate, kinetic energy.
Accordingly, it is desirable to provide a vehicular steering wheel and column assembly including a torsional friction damper that substantially reduces or entirely eliminates the occurrence of SRS. It would also be desirable if, in certain embodiments, the torsional friction damper were integrated into a component, such as an SIR coil assembly, commonly employed in conventional vehicular steering wheel and column assemblies so as to reduce cost and overall part count. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.